Arctic (The or Regions): A term generally used to designate a vast area lying north of the Arctic Circle at 66.5ºN. It includes the Arctic Ocean as well as a great deal of land area above the Arctic Circle. This land area includes parts of northern Alaska (US), the high Canadian Arctic, most of Greenland (Denmark), northernmost Iceland, parts of Scandinavia and the extensive Russian Arctic.

Arctic Circle: A fixed point on the earth's surface at 66.5ºN designating the point at and above which, due to the curvature of the earth, there is at least one day per year of total light. During the periods of total light, the sun never "sets." Rather it circles the horizon, higher in the south and lower in the north. At the North Pole only, the sun appears to circle equidistant from the horizonduring periods of total light.

Arctic Ocean: Also called the polar sea; the vast ocean surrounding the north polar axis. Openings are through the Bering Strait between Alaska and Russia to the North Pacific; through Smith Sound between Greenland and Ellesmere Island (Canada) and through the Greenland Sea to the North Atlantic.

Degrees: A unit of measurement on the earth's surface. One degree of latitude [ º ] equals60 minutes[ ' ] of latitude or 60 nautical miles. However, degrees of longitudeare more widely spaced at the equatorand converge at the poles; therefore, there is no fixed unit of measurement for degrees of longitude.

Equator: 0º latitude. The equator divides the globe into northern and southern hemispheres.When the sun is over the equator, on approximately March 21 and September 21, days and nights are of equal length.These two days are designated as the Vernal, or spring, Equinox and the Autumnal, or fall, Equinox.

Geographic Miles: See nautical miles

Greenwich Mean Time (GMT): See universal time (UTC).The name Greenwich Mean Time was derived from the 0º longitudinal line or the Greenwich Meridianthat passes through Greenwich, England. Time "begins" at the Greenwich, or Prime, Meridian.

International Date Line: A line in the Pacific Ocean running roughly along the 180º meridian. The International Date Line is at the opposite side of the earth from the Greenwich, or Prime, Meridian and designates a time change. "Time" is one day later to the west of the International Date Line and a day earlier to the east.

Latitude: .Parallels or degrees of latitude (the east-west lines) are equidistant throughout the globe. Degrees of latitude are 60 nautical miles [69 statute miles] apart.

Longitude: .Because of the curvature of the earth meridians, or degrees of longitude (the north-south lines) are not equidistant; they are furthest apart at the equator and converge at the north and south poles.

Meridians: See Longitude. Meridians and lines of longitude mean the same.

Minutes: One minute [ ' ] of latitude equals 1/60th of a degree of latitude, or one nautical mile.

Nautical miles: One nautical (also called geographic) mile equals 6076 feet, or 1852 meters. As a rule of thumb, to convert nautical miles to statute miles, multiply nautical miles by 1.15. One knot designates a speed of one nautical mile per hour.

North Magnetic Pole: Also called Magnetic North; magnetic compasses point to Magnetic North, a mineral deposit in the High Canadian Arctic. Maps, however, are based on True North. In lower latitudes, the angular difference between True North (the North Geographic Pole) and Magnetic North is compensated for by a value known as Magnetic Variation. But to further complicate matters, Magnetic North is not a fixed point but is constantly on the move. Magnetic variation must be recomputed on a regular basis. In the past 100 years, Magnetic North has wandered approximately 600 miles to the north to its present location near Ellef Ringes Island in the Canadian Arctic.

North [Geographic] Pole: 90ºN or the North Pole; the north geographic axis of the earth where all lines of longitude converge. At the North Pole, there are six months of "day" and six months of "night." However, since all lines of longitude converge at this point, there are no time zones. Universal time generally is used at the North Pole. The North Pole lies in the Arctic Ocean where the polar ice pack is constantly in motion moved by wind and currents. Therefore, there is no permanent means of marking the location of the North Pole. The North Pole is also referred to as True [as opposed to Magnetic] North.

Parallels: See Latitude. Parallels and lines of latitude mean the same.

Polar Circle: the Polar Circle, generally designated as being at 80ºN, is a more or less arbitrary point used to designate the area around the north geographic pole at 90ºN. Polar and Arctic are not synonymous. Anything that is polar is also arctic; but not everything that is arctic is also polar. However, "polar" sometimes is used as a generic term simply to designate places with very cold climates.

Polar Regions [North]: Generally anything north of 80ºN is considered polar. Although a great deal of land lies above the Arctic Circle, only parts of nothernmost Axel Heiberg and Ellesmere Islands (Canada), northern Greenland, northernmost Svalbard (Norway), Franz Josef Land (Russia), and Severnaya Zemelya (Russia). lie above 80º. Regions can be both arctic (above 66.5ºN) and polar(above 80ºN), but the term usually designates only the Arctic Ocean (sometimes referred to as the Polar Sea) and land areas immediately bordering it.The north polar region consists of water, the Arctic Ocean, bordered by land. The south polar region, on the other hand, consists of land, the continent of Antarctica, surrounded by water, the Southern Ocean.

Polar Ice Pack: The permanent floating ice pack over the Arctic Ocean. The permanent ice pack tends to recede in summer and expand in winter to touch most of the land areas bordering the Arctic Ocean. However, the amount can vary significantly from year to year.

Polar Sea: see Arctic Ocean. Polar Sea is an older term for the Arctic Ocean. Arctic Ocean now is the preferred name although Polar Sea is still sometimes used.

Tropic of Cancer: 23.5ºN latitude.This line designates the furthest north of the sun's apparent travel over the earth's surface. The longest day of the year in the northern hemisphere and the shortest day of the year in the southern hemisphere, approximately June 21, occur when the sun is over the Tropic of Cancer.

Tropic of Capricorn: 23.5ºS latitude. This line designates the furthest south of the sun's apparent travel over the earth's surface. The longest day of the year in the southern hemisphere and the shortest day of the year in the northern hemisphere, approximately December 21, occur when the sun is over the Tropic of Capricorn.

True North: see North [Geographic] Pole.

Universal Time (UTC): The sun's apparent travel over the earth's surface from east to west is at the rate of 15º of longitude per hour. Time zones are established roughly every 15º of longitude so that local times correspond to the hours of day and night. Greenwich Mean Time, or the newer term Universal Time--made necessary by space travel--is a single coordinated time standard throughout the globe. For example, in the Eastern Time Zone, add 5 hours to Eastern Standard time for Universal Time, and 4 hours to Eastern Daylight time.

Zulu Time (Z): The letter "Z" is the symbol for Greenwich Mean Time, or the newer Universal Time. In the standardized phonetic alphabet, the letter "Z" is spoken as "zulu."